The sun sets behind the Kukulkan pyramid in Chichen Itza, Mexico, where
the last stone monuments were carved prior to the collapse of the Maya civilization.

Archaeologists have long suspected that climate change may have caused droughts that brought the agriculture-based Maya civilization to its knees. A new study published in Science last week bolsters this theory with new physical evidence, showing that ancient droughts correspond with political upheaval as recorded in stone carvings.

Scientists generally figure out what long-ago climates looked like by measuring oxygen isotopes in sediment samples. These isotopes are variations on the oxygen atom that have eight, nine, or ten neutrons, depending on the amount of water present when the sediment was deposited. A sediment layer’s ratio of heavy versus light oxygen isotopes can tell scientists when the layer was formed and what the climate was like at that time. Researchers in past studies have relied on sediment cores from lakes or oceans, but the researchers in this study used a stalagmite from a cave near the ancient Maya city of Uxbenká, in present-day Belize.

Protected by the cave, the stalagmite’s layers were better preserved than those from the bottom of a lake or ocean. Plus, the data derived from these layers were much more detailed. The scientists were able to see what the climate was like in Mesoamerica over the past 2,000 years, and zoom in to intervals as short as 6 months.

The scientists compared their new and improved climate timeline with historical records the Maya carved into nearby stone monuments and found some interesting overlap. A period of unusually wet conditions in the mid-fifth century coincides with carvings that describe a major population boom and the expansion of political centers. A drying trend in the later half of that century corresponds to records of political disintegration and warfare. For 80 years after the dry spell, climate records indicate extreme drought conditions, and the concurrent lack of stone monuments suggests that Mayan leaders were no longer commissioning them to be carved. With this new physical evidence of a climate change-related collapse, the researchers have reinforced theories that the once-great Mayan civilization dried up sometime between 1020 and 1100 A.D.

How can they figure 6 month intervals? I mean the water that creates a stalagmite started its journey from the surface some huge variable length of time before.

jd

Depends on the cave. For some, it can take 1000s of years. but there are some caves near where I live that are in such porous rock that the water dripping off the stalagmites is practically in real time with the rain.

geack

As jd says, the time it takes water to get from the surface to the stalagmite isn’t necessarily huge, plus it’s not necessarily variable. Barring major geologic changes, water penetration can remain fairly constant. So even if the time from surface to stalagmite is large, once you have a good idea what it is, you can correlate the stalagmite deposits to the surface activity. The rate at which a stalagmite grows relative to the rate of water flow is also reasonably consistent. Apparently the researchers were able to establish these two variables in this location with sufficient precision to allow them to “read” the deposits at 6-month resolution. I assume this was due to local geology that results in very consistent penetration and deposition rates. At other places such resolution would likely be impossible.

Kevin N

You don’t need to come up with climatological reasons why a civilization perished. It’s composed of people. Any number of things can go wrong.

Pippa

Collapse of any civilisation is likely mutifactorial, but identifying the major changes that go towards forcing a civilisation in the direction of tumultuous change and collapse can be helpful – especially as one or more are likely to be the tipping point. If only we showed more evidence of learning from the lessons that history can teach us.

http://thailandrocks.com chiangraiken

I would venture it’s just as much due to over-harvesting of resources in the vicinity of villages. People are still doing so currently. In Middle East regions, the eco-devastation of centuries ago was more devastating because they started with a Mediterranean eco-system which was readily over-harvested. At least the Maya had a jungle environement which was a bit more resilient, and didn’t devolve to pure desert as the Middle East did.